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Discussion Starter #1
I expected my fuel economy to drop as anytime you add more air you add more fuel to get more bang it'll drop. But I've gone from a combined average of 18-20 to a now combined average of 13-15. Same driving route and habits. Only thing I've changed is I now have 20in SRT Alcoa wheels instead of the 18in Magnum 500 wheels and Brembo brakes. I used the Trinity to change my wheel size and I am running 275/45 out back.

Going to the 20in wheels has actually lowered my RPM in all gears, M6 and 3.73 diff, so I thought maybe I'd gain some MPG back from that.

In 6th running 65MPH I might be turning 1400-1500 RPM. I do detect a slight surge when the motor goes under a light load like up an incline. If that is the SC going into boost then would I be better off running a little higher RPM in 5th? I do not detect any surge when running the higher RPM.

I guess basically I am trying to figure if I need to change my driving habits. I used to keep the RPM pretty low when I was just cam/heads/headers. But trying to figure if I'm in boost or in bypass and if I need to keep higher RPM now or not is difficult. Also, watching the Trinity it would appear that even though I am at lower RPM in 6th the fuel pulse width seems to be larger. About 1k to 2k more than in 5th with the higher RPM.

This is my daily driver and I can live with this lower MPG but if I can figure a way to get some more MPG out of my car that would as always be beneficial. Part of the reason I went with the SC over a turbo is that it was advertised as having a bypass valve so that fuel economy would be less effected than if it stayed in boost all the time.

Thanks y'all.
 

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How about getting a boost gauge? This way you can see visually what puts your car under boost during normal driving and then you could change your driving habits based off of that.
 

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How about getting a boost gauge? This way you can see visually what puts your car under boost during normal driving and then you could change your driving habits based off of that.
+1 to this. A gauge can provide helpful information.

My mileage has actually increased with a supercharger, but there are so many factors involved - it's hard to give a really helpful answer without knowing more.

- Matt
 

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Discussion Starter #4
I'm in the process of switching all my data logging over to the ZT-2 instead of the Trinity. It just cost a fair chunk to get the sensors and LCD gauge to display it all. I did have that synthesized boost gauge setup on my Trinity but it was off. On the dyno I showed a little over 8lbs of boost whereas my Trinity never showed anything more than 6lbs.

So I guess that'll do for now then. I will get everything setup for the ZT-2 and see precisely when, where, and how I go into boost and adjust from there.
 

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Will you have the ability to monitor the AFR as well with the ZT-2 setup? If you're running rich all the time, you may have to tweak the tune. That certainly may not account for your drastic drop in mileage, but again - more information is better.

- Matt
 

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The other thing is not loading the engine (low rpm/higher gear) as this may fool the PCM into interpreting this as higher load and more enrichment (or knock sensors tripping on, retarding timing).

When I was doing data logging for my tune, when the engine was loaded up at lower rpm, the spark knock readings went way up...

There's also the drag of the supercharger, and your tuning (more enrichment), so that's going to have an impact.

OEM S/C engines typically take a hit on MPG ratings vs. their NA counterparts.
 

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my experience with all the superchargers we have installed and the superior tuning from AJ and the tuning folks at API, is better than expected fuel economy, and in some case significantly better than expected, on my own, if i baby it on the hwy, i get 24 to 25 easily and my Challenger is tuned quite agressivelly
Luke
 

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Discussion Starter #8
Will you have the ability to monitor the AFR as well with the ZT-2 setup? If you're running rich all the time, you may have to tweak the tune. That certainly may not account for your drastic drop in mileage, but again - more information is better.

- Matt
With the ZT-2 I can monitor everything. The ZT-2 box can be piggy backed so that you can monitor literally as many functions as the car has and sensors are available for. In the short term I am going to get their boost sensor and hook that to the ZT-2 and just monitor A/F and boost. I've thought about adding another ZT-2 so I can monitor fuel pressure and maybe EGT as well. I already am monitoring A/F and it stays around the 14 mark unless I get into the throttle or boost then it richens up quite a bit. I will have to hook it up and look at what it drops to as right now I don't remember.

The other comments in this thread about gas mileage either barely decreasing or in some cases increasing is what has prompted me to posit this question. It has been quite unexpected to see my fuel consumption increase this much.
 

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Same as above, all of our experience with installing and tuning superchargers and turbos on these cars has been an improvement on mileage, including the E force system.
 

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I'm thinking your new rims are a contributor to your decrease (vs. the supercharger) For example, I supercharged my Avalanche and went to 20" rims and bigger rubber. Lost 100 RWHP (had it dyno'd), and could watch the gas gauge drop. I was amazed/dismayed at the negative effect of beefing up rims and tires.
Try slapping your old rims on and see what the difference is.
 
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The factory SRT Alcoa wheels with tires and sensors were 6lbs lighter for each wheel than my 18 wheels and tires on my last car.
 

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Discussion Starter #12
I'm thinking your new rims are a contributor to your decrease (vs. the supercharger) For example, I supercharged my Avalanche and went to 20" rims and bigger rubber. Lost 100 RWHP (had it dyno'd), and could watch the gas gauge drop. I was amazed/dismayed at the negative effect of beefing up rims and tires.
Try slapping your old rims on and see what the difference is.
Unfortunately I can't. I upgraded to Brembo brakes thus the up size to the 20in Alcoa wheels. I really had no interest in getting 20in wheels but essentially I had to at the time.
 

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I'm not an expert by any means but maybe the supercharger tune that presumably came with your Trinity could use some tweaking. I leave stuff like that to the pros after my adventures with muddling with my Predator settings back in the day.

I also noted that my foot got a bit heavier after supercharging - especially to get around the "In The Way People" (Bill Burr).

At the end of the day you have a way cool supercharged RT. MPG? - Meh.
 

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Discussion Starter #14
I'm not an expert by any means but maybe the supercharger tune that presumably came with your Trinity could use some tweaking. I leave stuff like that to the pros after my adventures with muddling with my Predator settings back in the day.

I also noted that my foot got a bit heavier after supercharging - especially to get around the "In The Way People" (Bill Burr).

At the end of the day you have a way cool supercharged RT. MPG? - Meh.
The MPG and tracking thereof is more a diagnostic tool than an actual concern about fuel consumption. If my tune is off, ie rich, and thus robbing me of power for the sake of a safe tune I would rather get them extra horses freed up. Thank you for calling my R/T way cool. I agree. When I look at the credit card statements I get a bit down but then I just take the car for a ride!

:bouncy:
 

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Discussion Starter #16
Hopefully this coming week I can take it up there. I plan on leaving it with them for a whole day or two so that they can get the tune dialed in perfectly. They asked me to wait till the end of the month so they could get caught up after the holidays. I was using the forums as sounding board so as to not sound completely off my rocker when I complain about poor gas mileage versus other experience. Hopefully that will help my tuner look at the tune and be smarter, faster, better.
 

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Discussion Starter #17 (Edited)
delete post. replied to something i already replied too.
 

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Discussion Starter #19
It looks like whether I cruise in 6th @ 1600-1700RPM or 5th at around 2000RPM the fuel usage is pretty much the same. I have lost 1-2 mpg on my daily commute.

I just got my car back from the shop with a new tune. I'll have to run a couple of tanks to see if there is any change. I will say the new tune is a lot smoother. He said the Edelbrock tune was way conservative on timing and he bumped it up a good bit and was still on the conservative side. He know this is my dd, kids to daycare, and grab groceries car. So I'm pleased with a 500+ whp grocery getter with a conservative tune. Time will tell on the fuel consumption side.

I've been getting a purge valve wrong flow CEL so my gas cap or something may be leaking. That would hurt too. So too many variable right now.
 
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